Women should go “low carb” if they want to conceive – because doing so could increase the chance of success by five times, say fertility experts.

They say one portion a day is the limit for those trying to conceive, and advised cutting out all white bread, pasta and breakfast cereals.

Leading doctors said they are advising patients with fertility problems to radically change their diet, after evidence showed that high amounts of refined carbohydrates can seriously damage conception chances.

British clinics yesterday revealed that they have begun enrolling patients on nutrition courses and even cookery classes, amid concern that increasingly stodgy diets are fuelling fertility problems.

Dr Gillian Lockwood, executive director of fertility group IVI, said she advises all patients to cut their carbohydrate intake, amid a growing body of evidence linking such foods to impaired fertility.

High levels of carbohydrates – especially refined ones – are already known to affect the body’s metabolic functions, and can fuel obesity, which in itself reduces fertility.

But experts said there is growing evidence that a typical western diet, with high reliance on convenience foods, high in carbohydrates, badly affects a woman’s reproductive system, reducing the quality of her eggs.

Fertility experts advised all couples trying to conceive to look closely at their diets – and said there was strong evidence that women in particular should cut back on carbohydates.

Dr Lockwood highlighted research which found women with lower carbohydrate intake had four times the success rates of those on standard diets.

The US trial on 120 women undergoing IVF split them in to two groups, depending on the balance of protein and carboyhydrate in their diet. In total, 58 per cent of those in the “low carb” group (meaning at least one quarter of their diet was protein) went on to have a baby.

In the “high carb” group, where less than a quarter of daily energy came from protein, just 11 percent achieved success, the study by the Delaware Institute for Reproductive Medicine (DIRM) in Newark found.

Researchers concluded that those trying for a family should aim for up to 35 per cent protein and less than 40 per cent carbohydrates.

Dr Lockwood, from IVI Midland, in Tamworth, said she now advised all patients to go “low carb”.

“They should be eating plenty of fresh vegetables and protein and limiting their carbohydrate intake to just one group and portion a day.

“I tell my patients that if they are going to have toast for breakfast, then that is their carbs for the day. They cannot then have a sandwich for lunch and pasta for dinner.

“If they want a pasta supper that has to be their carb, or if they want a jacket potato for lunch, then that is it.”

Women were also advised to eat dairy foods as cholesterol is the ‘building block’ for all the reproductive hormones, she said.

Today’s typical diet was storing up fertility problems, she said.

“Modern food is very carb-rich, tasty and cheap, so it’s easy to see why people tend to eat a lot of this food. But it is also very low in nutrition,” she added.

“The women’s partners also need to do their part and scrap their stuffed-crust pizza and enjoy a chicken salad too,” she said.

Leeds Fertility last month began giving infertile couples four lessons in nutrition – including cookery classes, to encourage them to cut the carbohydrates, and introduce a more varied diet.

Grace Dugdale, the reproductive biologist leading the scheme, said couples trying for a baby should cut out all white bread and pasta, and switch to wholemeal versions.

She suggested replacing processed breakfast cereals with eggs, or natural yoghurt and fruit, and advises swapping lunchtime sandwiches with carb-free salads. When carbohydrates were consumed, unprocessed was best, she said, recommending muesli and porridge over sweetened cereals.

Couples should try to stick to just one portion of carbohydrates a day she said – and make it a complex one, such as brown rice or wholewheat pasta.

Miss Dugdale said: “People should be cautious of the refined carbohydrates in white bread, pasta, cereals, biscuits and cakes because their simpler molecules break down more quickly in the body, causing a spike in blood sugar.

“Over time the body becomes less able to process sugar, leading to poor metabolic health, which can cause inflammation in the body and damage mitochondria, the powerhouses of the cells.

“A woman's eggs are very large cells with a high number of mitochondria, so their quality is affected. Poor diet that includes refined carbohydrates can also affect male fertility by damaging the DNA in sperm. This affects sperm motility, their ability to swim, their morphology, or the shape which makes them good swimmers, and the sperm count, or how much sperm is produced.

“A diet low in refined carbohydrate is therefore important for both the man and the woman.”

The scheme led by Balance Fertility, a research company looking at lifestyle and underling factors behind infertility, will be expanded in September, with patients getting individual consultations to look at their diet and lifestyle in detail.

Prof Adam Balen, chairman of the British Fertility Society, said all couples could give their fertility the best chance by eating a healthy diet, and looking in particular to cut carbohydrate levels.

He said: “We know that diet has a major impact on chance of conception and on egg quality and increasingly it seems that carbohydrates play a particular role.”

And he said those struggling with fertility problems should undergo individual consultations to check levels of key nutrients, vitamins and minerals.

The British Dietetic Association said further research into the area was needed. A spokesman said: “As dietitians we don’t promote demonising nutrients, but paying attention to diet, encouraging moderation and portion control both pre and during pregnancy are extremely important for mum, dad and baby.”